I’d like to lecture to my large classroom using a mic attached to my MAC and the speaker system in the lecture hall. I do not want to record it ahead of time, but I don’t care if I record the entire 75min of lecture in addition to broadcasting it live. I see several options for recording but I can’t tell if any broadcast at the same time. I cannot directly connect a mic to the lecture hall audio, but I can play sound on it if I connect up to my headphone jack. Is there any way to do this?
— David Hanson
A quick search turned up "Line In," a bit of freeware. Does it do what you want?
http://www.rogueamoeba.com/freebies/
The correct keywords make all the difference. I think this may work. It is the correct concept, I just have to balance the feedback.